Usually, a transmission network that is a communication network for connecting a, gateway and a base station exists on a network of a cellular phone service. In order to achieve a reduction in the costs and an increase in the capacity for the transmission network at the same time, there are many examples in which the transmission network is constructed by an Ethernet (registered trademark). In this case, an operation manager uses a virtual LAN (VLAN) to produce a virtual communication path that connects the gateway and the base station.
Up to now, when such a virtual communication path is manually produced, there is frequently used a configuration in which all of switches within the Ethernet are multiplexed with the VLANs, and a pertinent VLAN is selected by a port that is connected with the gateway or the base station. In this configuration, because a difference in setup between the switches is reduced, the setup work amount is suppressed.
However, in this configuration, because all of the switches are multiplexed by the VLANs, a broadcast frame and a multicast frame are transferred to all of the switches. As the number of base stations accommodated in the transmission network increases more, the number of multiplexed VLANs also increases more. This suffers from such a problem that frames of different VLANs are superimposed on each other to deteriorate a communication quality on the network.
WO05/112356 discloses a shortest path calculation system that minimizes the multiplicity of the VLANs in order to solve such a problem when all of switches are multiplexed by the VLANs. In this system, the network management server first obtains the shortest path between the gateway and the base station according to topology information on the network. The network management server then allocates the VLAN to a connection port between the switches on the shortest path, and produces a virtual communication path having the same form as that of the shortest path.
When the virtual communication path is produced through the shortest path calculation system, a transfer range of the broadcast frame and the multicast frame can be limited to the shortest path between the gateway and the base station. As a result, the communication quality is prevented from being deteriorated. Also, because a VLAN configuration process is automated, the operation work amount can be reduced.
The shortest path calculation system requires the topology information in order to obtain the shortest path. The topology information is obtained from the gathering of link information representative of a connection relation between two switches which are connected directly to each other. In order to automatically gather the link information from the switches within the network, there is used a control protocol between the switches such as a link-state type dynamic routing protocol or a link layer description protocol (LLDP) which is defined in “802.1ab—Station and Media Access Control Connectivity Discovery,” IEEE Standard for Local and metropolitan area networks, IEEE, May, 2005.
Each of switches within the network periodically transmits a frame for exchanging a node identifier with that of an adjacent switch according to the control protocol. Then, the switch extracts a node identifier of the opposed switch from a frame received from the opposed switch, and automatically produces the link information of a link provided in the switch. The network management server gathers the link information produced on the switches from all of the switches within the network, and combines the link information together to produce the topology information on the network.